Industrial air valve with valve body having flexible sealing lip

ABSTRACT

There is herein disclosed an industrial type air valve assembly in which poppet type valve heads have a new and improved selfcompensating sealing lip and are controlled by a new and improved solenoid operated pilot valve. The pilot valve is connected to an operating solenoid in a manner providing a no-load gap between a valve stem and a valve head to reduce starting load. The valve stem is supported by plastic bearing means providing minimal frictional loading to further reduce starting load. The valve stem and valve head cooperate to provide variable force transfer surfaces whereby pressure forces opposing movement of the solenoid armature are varied from a minimum pressure force prior to opening of the valve providing minimum resistance to the armature to a maximum pressure force immediately after opening of the valve to decelerate the armature to an intermediate pressure force to brake the armature as it bottoms.

United States Patent [191 Cagle [451 Sept. 25, 1973 INDUSTRIAL AIR VALVEWITH VALVE BODY HAVING FLEXIBLE SEALING LIP 3,118,470 l/l964 Peras137/625.27 X

Primary Examiner-Arnold Rosenthal Atlorney--Harness, Dickey & PierceInventor: Harlan R. Cagle, Clarkston, Mich.

Assrgnee: Sahhn Engineer ng Company, Inc., {57] ABSTRACT Birmingham,MlCl'l.

There is herein disclosed an industrial type air valve as- 1970 semblyin which poppet type valve heads have a new Appl. No.: 100,471 andimproved self-compensating sealing lip and are controlled by a new andimproved solenoid operated Related Apphcauon Data pilot valve. The pilotvalve is connected to an operating Division of Ser. No. 880,061, Nov.26, 1969, Pat. No.

solenoid in a manner providing a no-load gap between a valve stem and avalve head to reduce starting load. The valve stem is supported byplastic bearing means providing minimal frictional loading to furtherreduce 3,582,039, which is a continuation-in-part of Ser. No. 639,545,May 18, 1967, abandoned.

2% 5 251/ starting load. The valve stem and valve head cooperate T 62 63to provide variable force transfer surfaces whereby 1 0 can 625 pressureforces opposing movement of the solenoid armature are varied from aminimum pressure force prior 5 6] References Cited to opening of thevalve providing minimum resistance to the armature to a maximum pressureforce lmmedl- UNITED STATES PATENTS ately after opening of the valve todecelerate the arma- 3,3l5.696 4/1967 Hunter 251/63 X ture to anintermediate pressure force to brake the ar 3,l66,358 l/l965Valentine.... l37/625.27 X mature as it bottom5 3,463,192 8/1969 Herion,Jr... l37/625.25 X 3,608,587 9/1971 Zbell l37/625.66 2 Claims, 4 DrawingFigures 1; M M 42 12 M 74 7! p A 72' 7 74 1? 4 I! J! 54 2 v I /44 M /4/11 Ml BACKGROUND AND PRIOR ART This application is a divisional of mycopending application Ser. No. 880,061 filed Nov. 26, 1969 now U.S. Pat.No. 3,582,039, which is a continuation-inpart of my prior applicationSer. No. 639,545 filed May 18, I967, and now abandoned. y

In the prior art, poppet valves and solenoid operated pilot valves havebeen widely used in applications requiring relatively few cycles ofoperation. In adapting prior art poppet valves and solenoid operatedvalves to usage in an air control valve unit of the type described inU.S. Pat. No. 3,474,825 with swingingarm press unloading apparatus ofthe type disclosed in U.S. Pat. No. 2,609,776, I have found that thefastoperation and .repetitive cycling to which these valves aresubjected causes excessive failures in both the valving and theelectrical components. In particular, the poppet valve heads, the pilotvalves and pilot valve bodies, and the pilot valve operating solenoidshave presented wear problems.

The unloading apparatus comprises a swinging arm which carries an airactuable jaw device between a lowered position adjacent a press cavityand a raised position located upwardly and outwardly from the press. Theswinging arm is moved from the lowered position to the raised positionby a single acting air operable power cylinder to which high pressureair is selectively directed. The swinging arm is lowered at a controlledrate as the high pressure air is exhausted from the cylinder. The jawcarried by the swinging arm is positively closed and opened, to gripandrelease a workpiece, by means of a double acting air operable powercylinder to and from which high pressure air is selectively directed andexhausted to obtain the opening and closing movements of the jaw.Ordinarily, with the swinging arm initially in the lowered position, theoperational sequence is: (I) extend and close jaw to grip workpiece, (2)swing arm upwardly and carry workpiece from press, (3) open jaw torelease workpiece, and (4) return arm to lowered position.

The air control valve unit is connected to a single high pressure airline, extending from a source of high pressure air, through a commoninlet chamber in a valve housing containing an inlet and exhaust valveassembly for the single acting arm cylinder, an arm cylinder speedcontrol valve, and a pair of inlet and exhaust valve assemblies for thedouble acting jaw cylinder. These valve assemblies are sequentiallyoperated to control flow of high pressure air from the common inletchamber to the arm cylinder and the jaw cylinder to effect theaforedescribed operational sequence.

The unloading device and associated valving are primarily utilized inlarge factories which have a conventional industrial type high pressureair supply. Such an air supply is subject to variations in pressure. Itis common design practice to assume variations of between approximately40 psi and 150 psi. Industrial air valves are commonly designed foroperation with lubrication supplied by an oil mist introduced in the airupstream of the valve by special lubrication apparatus. One type offailure of industrial valves is from lack of proper lubrication whichmay result from failure to replenish oil in the special lubricationapparatus or by failure of the lubrication apparatus itself. Of course,failure of industrialvalves is highly objectionable not only because ofthe cost of maintenance or replacement but also because of the resultinginterruption of production.

In the prior art, industrial air valves of the present .type have beenrated as having approximately a 10 to 14 million cycle life expectancywhile the solenoids utilized to operate the pilot valves have been ratedas having approximately a 5 to 10 million cycle life expectancy. Inactual practice, many of these valves and solenoids fail far in advanceof the expected life expectancy.

SUMMARY OF INVENTION It is the primary purpose of this invention toprovide a new and improved industrial air valve including anelectrically operated pilot valve assembly for use with apparatusrepetitively cycled through relatively short operational cycles overlong periods of time.

I have discovered that many industrial air system parts requiringsealing means, such as valve heads, plugs, plates, bearings, end walls,and pistons, heretofore made of machined metallic parts and mountingseparate sealing means, such as O-rings, packings, wipers, and the like,may be advantageously made in one piece from a plastic material such asa fluorocarbon polymer. Furthermore, in adapting one-piece plastic partsfor use in industrial air systems, I have discovered that exceptionallyeffective seals can be provided by integrally forming air pressureactuable sealing lips on a one-piece part in a new and improved mannerproviding for self-compensation for wear in use over exceptionally longperiods of time.

The invention further resides in the provision of a solenoid operatedvalve in which the number of parts is greatly reduced, the startingforce on the solenoid is greatly reduced, the friction load on thesolenoid is greatly reduced, and resistance to bottoming of the solenoidis minimized while reducing the bottoming force. Furthermore, new andimproved mounting means have been provided and a manual operator hasbeen incorporated with the solenoid apparatus. As a result of thisinvention, a solenoid controlled industrial air valve has been providedwhich will operate in excess of million cycles without failure.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a side elevational view, insection, of a control valve assembly incorporating the inventivefeatures;

FIG. 2 is an enlarged view of the pilot valve portion of the apparatusshown in FIG. 1;

FIG. 3 is an enlarged view of the poppet valve portion of the apparatusshown in FIG. 1;. and

FIG. 4 is an enlarged view of the poppet valve of FIG. 3 disassociatedfrom the valve bore.

DETAILED DESCRIPTION Referring now to the drawings, a control valve unitof the type disclosed in U.S. Pat. No. 3 ,474,825 illustrativelyembodies the inventive features. In general, a control valve assembly 10comprising poppet valve head portions 12, 14 is mounted in a valvehousing 16 for movement of the valve heads between open and closedpositions relative to an inlet-exhaust chamber 18. The general operationof these valve assemblies will be understood by those skilled in the artto which this invention relates and are described in further detail inU.S. Pat. No. 3,474,825 and hereinafter only to the extent required foran understanding of the present invention. Suffice it to say that thecontrol valve assemblies control flow of high pressure air to andexhaust air from opposite ends of air operated power cylinders and arealternately actuated between inlet and exhaust positions.

Control valve assembly comprises spaced valve head members 12, 14interconnected by a valve steam 58 so as to be operable as a unitbetween an inlet position, FIG. 1, whereat high pressure air isdelivered to the associated power cylinder and an exhaust position (notshown) whereat high pressure air is exhausted from the associated powercylinder. Movement of the valve assembly 10 is controlled by a pilotvalve assembly 20. An identical pilot valve assembly 22 controlsmovement of similar control valve assemblies (not shown). The pilotvalve assemblies are electrically operable to alternately connectpressure chambers 24, 26 to a source of high pressure air in chamber 28and to exhaust whereby the control valve assemblies are alternatelymoved by high pressure air in the pressure chambers between exhaust andinlet positions. Valve assembly 10 is shown in the inlet position withvalve head 12 seated and valve head 14 open. Spring means 30 bias thevalve assembly to the exhaust position (not shown) whereat valve head 12is opened and valve head 14 is seated.

Since the electrically operable pilot valve assemblies are identical,the reference numerals are hereinafter applied to one or the other butnot to both and it will be understood that each reference numeral isequally applicable to the corresponding part in the assembly notdesignated. Pilot valve means 32 and operating means 34 are mounted in ahousing 36 having a valve bore 38, an inlet passage 40 and check valvechamber 42, an inlet-exhaust passage 44 connected to pressure chamber24, and a solenoid cavity 46. An end plate 48 having a manual operatorbore 50 and cushion chamber 52 is adjustably fastened to the valvehousing by threaded fasteners (not shown) to secure the parts in thepositions shown. The pilot valve means comprises a combination bearingand end plug and sealing means member 54, a combination bearing and endplug and sealing means and valve body member 56, a combination operatorrod and valve stem 58, a valve head member 60, and a compression spring62. The operating means comprises an armature coil 64 and an armaturemember 66 mounted in an armature frame 68. A bore 69 in the framereceives the rod 58. A resilient O-ring member 70 separates the member56 and the armature frame 68 and acts as a vibration cushion. A manualoperator member 72 having an abutment plate portion 74 and a push pinportion 76 is spaced from end plate 48 by a resilient O-ring member 78which also acts as a vibration cushion.

In the normal position, shown by assembly 22, the armature is located inan extended position with an abutment plate portion 80 in abuttingengagement with abutment plate portion 74 of the manual operator.Referring now to FIG. 2, one end 82 of valve stem operator rod 58 abutsthe armature 66. High pressure air (e.g. 80 psi in the illustrativeembodiment) in a rod chamber 84 formed by a bore 85 in the end plug 54acts on the end 86 of the rod to bias the rod and the armature to theextended position. Rod chamber 84 is connected by a passage 87, formedbetween the rod 58 and the wall of the bore by the clearance(exaggerated in FIG. 2 for purposes of illustration) of a sliding fit,to an inlet chamber 88 between end plug portions of members 54, 56.Thus, the rod chamber 84 is the same as the inlet chamber with respectto the force effect of the high pressure air on the rod 58 which may heslidably supported in bore 85 or by any other suitable means. The highpressure in the rod chamber 84 and inlet chamber 88 is derived from ahigh pressure source (not shown) through inlet chamber 28 in valvehousing 16, a check valve 89, and inlet passage 40. Sealing lips 90, 92on the end plugs and sealing means 94, 96 on the valve head 32 closechamber 88 in the normal position. High pressure air in chamber 88 andcompression spring 62 hold the valve head in a closed position relativeto a passage 98 in a portion of member 56 and seated on an undercutvalve seat 100. Passage 98 connects pressure chamber 24 via a passage102 to an exhaust passage means 104, 105.

When coil 64 is energized, armature 66 is moved from the extendedposition shown by assembly 22 to a retracted position shown by assembly20. Simultaneously, the rod 58 is moved from the extended position tothe retracted position due to abutting engagement with the armature at82. Rod 58 is slidably supported in bearing portions of the members 54,56, which are formed by the bores 85, 98, by an end portion surface 106and an intermediate narrow width surface 108. The length of thesesurfaces are minimized to reduce friction. The length of surface 106 issuch as to provide sliding support throughout movement of the rod andthe length of surface 108 is such as to open exhaust port in theextended position and to close the exhaust port in the retractedposition. The reduced diameter portions of the rod 110, 112 adjacent thesurface 108 and the enlarged portion 113 of bore 98 serve to reducesliding friction.

An abutment flange 1 14 is provided on the rod to engage the valve headand move the valve head to the open position against the bias ofcompression spring 62 and high pressure air in chamber 88. A flangechamber 116 is formed in the valve head and has a depth substantiallygreater than the width of the flange so as to provide a substantial gap118 between the valve head and the flange in the extended position.Thus, the rod and armature are moved a substantial distance underminimum load at the beginning of movement. This arrangement may bereferred to as a no-load gap means which in effect provides lost motionmeans between the rod and the valve head. The only load is that causedby the force of the high pressure air in chamber 84 against the end ofthe rod (e.g. approximately lb. in the illustrative embodiment),frictional force between the rod and the valve head, frictional forcebetween the rod surface 106 and member 54, and frictional force betweenthe rod surface 108 and the member 56. When the flange 116 engages thevalve head surface 120, the additional load caused by the compressionspring (e.g. approximately k lb. in the illustrative embodiment) andhigh pressure air (e.g. approximately 3 lb. in the illustrativeembodiment due to 80 psi air pressure acting through a relatively narrowannular sealing surface on the valve head in engagement with the valveseat) acting on the valve head is encountered. Valve head 60 is moved tothe open position to connect inlet chamber 88 to passage 44.Simultaneously, the exhaust passage means 104 is closed so that highpressure air is delivered to the pressure chamber through passage 44.When the solenoid coil is de-energized, spring 62is effective to movethe valve headto the closed position. Movement of the valve headsimultaneously moves the rod toward the extended position due toengagement of surface 120 with flange 114. Also, the armature66 issimultaneously moved toward the extended position due to engagement ofthe end of the rod 82 with the end of the armature. When the valve head60seats on the valve seat 100, the momentum of the rod and high pressureair, acting in chamber 84 on the end 86 of the rod, move the rod andarmature to the fully extended position andiestablish the no-load gap 118 between the valve head and the flange.

One of the advantages of the present structure is that wear between theabutment plate portion 80 of armature 66 and the armature frame 68 isgreatly minimized. As is conventional, the abutment plate portion 80bottoms against the armature frame at 122 inthe fully extended position.In conventional valve designs, the armature bottoms with such force asto cause extensive wear and eventual failure of the solenoid. The reasonfor the reduction in wear and hence increased life of the solenoid inthe present structure appears to reside in the pilot valve design whichreducesthe bottoming force. As may be seen by reference to FIG. 2, thearmature 66 starts under essentially no-load conditions due to the gap118 between flange 114 and shoulder 120 as previously described. Theonly force resisting movement of the rod 58 and armature 66 is thatcaused by the high pressure air in chamber 84 against the end of the rodand by friction between the rod and the valve body which is quite small.When the rod flange 114 engages the valve shoulder 120, the armature andvalve rod are traveling at maximum velocity with maximum force. Thearrangement is such that maximum load is applied to the armature 66 uponengagement of rod flange 114 with valve shoulder 120. The maximum loadis equal to the pressure in chamber 88 acting on the sealing surfacearea as measured by the diameter of surfaces 96, 100 and the force ofcompression spring 62. However, the maximum pressure force is onlymomentarily applied through the valve head because as soon as the valveopens there is pressure equalization relative to the valve head. Thevelocity of the armature and its energy is substantially reduced by themaximum pressure force as the valve opens. Thereafter, another lesserpressure force .is applied through the valve rod as measured by thediameter of the sealing surface 108. The result is that the maximumforce of the solenoid armature is utilized to open the valve and much ofthe remaining force of the armature is dissipated before bottoming. Ineffect, the pressure force varies in accordance with the variations indiameter of the rod end 86, the sealing shoulder 100, and the sealingsurface 108. In the presently preferred form of the invention, thesediameters are approximately three thirty-seconds inch, one-fourth inch,and five thirty-seconds inch, respectively, so that in operation arelatively small pressure surface is effective prior to opening of thevalve, a relatively large pressure surface is effective immediately uponopening of the valve, and a pressure surface of intermediate size iseffective after opening of the valve to further retard the armaturemovement and reduce bottoming force. The advantage of the apparatus isthat a solenoid of smaller mately 1:5 :3. Thus, pressure differentialpermits opening of thevalve with minimal force, substantially shows thearmature. during opening of the valve, and then brakes the armatureprior to bottoming. With the present design a solenoid rated for a muchlesser maximum opening force may be utilized. In the presently preferredembodiment, a Model 02 Industrial Grade Sole- .noid rated at 5.5 poundsat 0 stroke, as manufactured by Detroit Coil Company under U.S. Pat.Nos. 2,466,592; 2,665,397; 2,671,187; 3,017,547; and 3,195,024 isemployed as the electro-mechanical actuator. While solenoids of thisgeneral type have heretofore probably had a life expectancy of between 5and 7 million cycles in the aforedeseribed environment, such solenoidshave been operated more than million cycles without failure inassociation with the pres- .ent valve design.

Tests of the pilot valve have shown that maximum wear tends to occurbetween the surface 108 and the bore 98 onopposite sides of the exhaustpassage 104. This wear may be substantially reduced by making the member56 from a conventional glass filled fluorocarbon resin (e.g. Teflon) inwhich the tiller comprises one or more additives such as 15-20 percentglass fibers and 5 percent graphite or molybdenum disulfide.

Another feature of the air valve of the present invention isincorporated in the control valve assemblies by providing one-pieceannular valve head members 12 formed of plastic material and havingintegral sealing means. The plastic material is a low water absorption,high wear resistant material having a low coefficient of friction andgood machining characteristics. The material is rigid in thick sectionsbut has sufficient flexibility in thin sections to permit high pressurefluids to deflect thin sections and create fluid seals with adjoiningsurfaces. Fluorocarbon polymer plastic materials such astetrafluoroethylene polymer and fluorinated ethylenepropylene polymerappear to be particularly well suited for this purpose. Teflon materialas manufactured by the E. I. DuPont Company has proved satisfactory. Thepresently preferred material is a commercially available mixture of thepolymer and approximately 15 to 20 percent glass fibers with 5 percentgraphite or molybdenum disulfide.

The sealing means takes the form of a generally axially extending,flexible, annular, sleeve-like lip formed by an undercut annular groove132 extending generally axially into the valve body and having a taperedouter side surface 134 outwardly inclined relative to the longitudinalaxis of the valve and providing an outer sealing surface band 136 ofsubstantial axial length toward the end of the lip.

The valve bore 138 is a relatively smooth cylindrical surface whichslidably receives the valve head 12. A traverse wall 139 extends acrossone end of the valve bore. The upper portion 140 of the poppet valve 12provides a transverse abutment surface 141 which acts as a piston inpressure chamber 24 and extends axially beyond the sealing means toprevent engagement between the sealing lip and the end wall 139. Whenhigh pressure air is supplied to the pressure chamber, the high pressureair acts on the valve head to move it parallel to the longitudinal axisof the valve bore against the associated spring 30 to seat a sealing rib142 on an adjoining valve seat 144 and to move a sealing rib 145 off ofits adjoining valve seat 146.

High pressure air in the pressure chamber also acts in the undercutgroove 132 on the sealing lip 130 to force the sealing surface band 136of the lip into sealing engagement with the adjoining wall 138 of thepressure chamber. The force exerted on the valve head by the highpressure air causes the sealing surface of the sealing rib 142 tosealingly engage the adjoining valve seat surface. When the valve headis moved in the opposite direction by the spring 30, a similar sealingengagement is effected between the sealing surface of the sealing rib145 and the adjoining valve seat surface 146.

In the presently preferred embodiment in the unflexed unstressedcondition of the poppet valve head 12 as shown in FIG. 4, the maximumoutside diameter as measured at the outer edge 150 of the flexible lipis 1.1 i .002 inch. The axial length of the groove 134 as measured at152 is nine thirty-seconds inch and the axial length of the base of thelip as measured at 154 is one-eighth inch. The radius at the base of thegroove at 156 is 0.024 inch. The inside and outside lip surfaces 134,160 extend at an angle of 10 relative to the longitudinal axis of thevalve head as measured at 162, 164, respectively. The outer edge of thelip is beveled at an angle of 60 as measured at 166. The diameter of thevalve bore 138 is 1.070 t .0005 inch. Thus, in the flexed stressedcondition shown in FIG. 3 the flexible lip is inwardly deflected toprovide a substantial axial length of engagement with the valve bore, asindicated at 168, with increasing outwardly directed resilient force inthe flexible lip from the base of the lip at 156 to the tip of the lipat 150. As a result, wear of the surface 134 does not cause failure ofthe valve head due to leakage of air past the sealing lip. Instead, thesealing lip provides self-compensating wear means whereby wear due tosuch factors as misalignment and sliding friction of the poppet valvehead in the valve bore is automatically self-compensated by theresiliently inwardly flexed lip structure. Poppet valve heads havingthis lip structure have been cycled in an air system without lubricationmore than 70 million times without failure which is 10 or more times theaverage life expectancy of prior art devices.

The angle 164 of the outer lip surface determines the amount of surfaceengagement between the valve head and the bore wall. At an angle of 25,which is believed to be approximately the maximum angle providingsufficientjsurface engagement for self-adjusting wear compensation, thetheoretical axial length of surface engagement in the illustrative valveembodiment is approximately 0.070 inch. At an angle of 7.20 which isbelieved to be approximately the minimum angle providing sufficientflexibility and fatigue strength in the lip, the theoretical axiallength of surface engagement in the illustrative valve embodiment isapproximately 0.265 inch. By way of example, at an intermediate angle of16, the theoretical axial length of surface engagement is approximately0.1 13 inch.

The dimensional characteristics of the flexible lip may vary within thelimits required for the necessary strengthyresilience, and flexibility.In the illustrative valve embodiment the thickness of the lip probablyshould be less than approximately 0.090 and greater than 0.040 inch. Theaxial length of the lip probably should be less than approximatelythree-eighth inch and greater than approximately one-eighth inch. Themaximum outside diameter of the lip probably should be less thanapproximately 1.16 inch and greater than approximately 1.11 inch. Whilethese dimensional characteristics are based upon a particular bore size,i.e. 1.070 in the illustrative embodiment, the general relationship ofthe various dimensions illustrates the necessary dimensionalrequirements to achieve the exceptional results of the present inventionand are believed to be generally relatively applicable to other specificembodiments.

. It is intended that the claims appended hereto be construed to covervariations of the illustrative embodiment which embody the inventiveprinciples herein disclosed except insofar as limited by the prior art.

I claim:

1. In the combination of a movable valve head and valve bore for use inan industrial air control system to control the flow of high pressureair by sliding axial movement of the valve head within and parallel tothe longitudinal axis of the valve bore between open and closedpositions relative to an air flow path and comprising an annular valvebore having a longitudinal axis and a transverse wall at one end, aone-piece annular valve body of self-lubricating flexible polymerplastic material, a transverse surface on one end of said valve bodylocated opposite said transverse wall of said valve bore and defining apressure chamber therebetween, an undercut annular groove in said valvebody opening at one end toward and into said pressure chamber andextending generally axially away from said transverse surface and saidtransverse wall into said valve body from a position adjoining saidtransverse surface and being closed and centrally terminating at theopposite end in said valve body, an annular sleeve-like flexible sealinglip integrally formed on said valve body by said undercut annular grooveand extending circumjacent and generally axially relative to said valvebody toward said transverse surface and said pressure chamber, an outersealing surface on said sealing lip extending generally axially towardsaid transverse surface and said pressure chamber and being outwardlyinclined relative to the longitudinal axis of said valve, and thediameter and the length and the angle of inclination of the sealing liprelative to the valve bore being such as to resiliently inwardlydisplace the sealing lip toward the valve body and form a self-adjustingaxially extending cylindrical band of surface engagement between thesealing lip and the valve bore, said band extending axially asubstantial length so as to maintain an effective seal notwithstandingthe eventual wearing away of portions of the sealing lip forming saidband, the axial length of said sealing lip from the closed end to theopen end of said groove being less than the axial length of said valvebody from the closed end of said groove to said transverse surfacewhereby said lip terminates axially inwardly a substantial distance fromsaid surface.

2. The invention as defined in claim 1 and the angle of inclination ofthe sealing lip'being approximately between 7 and 25.

1. In the combination of a movable valve head and valve bore for use inan industrial air control system to control the flow of high pressureair by sliding axial movement of the valve head within and parallel tothe longitudinal axis of the valve bore between open and closedpositions relative to an air flow path and comprising an annular valvebore having a longitudinal axis and a transverse wall at one end, aone-piece annular valve body of self-lubricating flexible polymerplastic material, a transverse surface on one end of said valve bodylocated opposite said transverse wall of said valve bore and defining apressure chamber therebetween, an undercut annular groove in said valvebody opening at one end towArd and into said pressure chamber andextending generally axially away from said transverse surface and saidtransverse wall into said valve body from a position adjoining saidtransverse surface and being closed and centrally terminating at theopposite end in said valve body, an annular sleeve-like flexible sealinglip integrally formed on said valve body by said undercut annular grooveand extending circumjacent and generally axially relative to said valvebody toward said transverse surface and said pressure chamber, an outersealing surface on said sealing lip extending generally axially towardsaid transverse surface and said pressure chamber and being outwardlyinclined relative to the longitudinal axis of said valve, and thediameter and the length and the angle of inclination of the sealing liprelative to the valve bore being such as to resiliently inwardlydisplace the sealing lip toward the valve body and form a self-adjustingaxially extending cylindrical band of surface engagement between thesealing lip and the valve bore, said band extending axially asubstantial length so as to maintain an effective seal notwithstandingthe eventual wearing away of portions of the sealing lip forming saidband, the axial length of said sealing lip from the closed end to theopen end of said groove being less than the axial length of said valvebody from the closed end of said groove to said transverse surfacewhereby said lip terminates axially inwardly a substantial distance fromsaid surface.
 2. The invention as defined in claim 1 and the angle ofinclination of the sealing lip being approximately between 7* and 25* .